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122
CHAPTER 18
18.35
From
( )
max
1
t
e
QQ
τ
−
=−
, we have at
0.900 s
t
=
,
0.900 s
max
Q
e
Q
−
10
=
.
6
0
0
Thus,
0.900 s
0.400
e
−
=
, or
()
ln 0.400
0.900
s
−=
giving the time constant as
0.
982 s
ln
900 s
0.
0.400
=
18.36
(a)
max
R
I
ε
=
, so the resistance is
4
3
max
48.0 V
9.60
10
0.500
10 A
R
I
==
=×
×
RC
Ω
The time constant is
=
, so the capacitance is found to be
5
4
0.960 s
10
F
10.0 F
9.60
10
C
R
1.00
µ
−
×
=
=
×Ω
(b)
( )( )
max
10.0 F
48.0 V
480 C
QC
=
1.92 s
t
=
, so the charge stored in the capacitor at
is
1.92 s
2
0.960 s
max
1
480 C
1
480 C
1
415 C
t
e
e
e
µµ
−
−
−
=
− =
−
=
18.37
(a) The current drawn by each appliance is
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 Spring '09
 Physics, Current, Work

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